There are two important parameters for a scanning optical equipment: highest resolution and maximum scanning width. For the same optical electronic converter (a CCD, for example), a design with a larger scanning width is obtained at the price of a lower resolution; on the other hand, to obtain higher resolution, the designer has to decrease the scanning width. Hence, to satisfy user's requirement of high resolution, manufacturers produce high resolution scanning optical equipment either with narrow scanning width or with a costly CCD that provides high resolution. On the other hand, to satisfy users' requirement of larger scanning width, manufacturers produce scanning optical equipment that has low resolution but increased scanning width. Majorities of users need to sometimes scan both high resolution pictures and wide size documents; which means that they have to own either two scanning optical equipments, one offers high resolution and one offers larger scanning width, or one scanning optical equipment which offers both but costs a lot. Thus users' financial burden is increased significantly. Hence, some manufacturers developed lens sets for scanning optical equipment. They also obtained patents for the lens sets, such as publication number 232398 for "multi-lens switching mechanism," and publication number 235112 for "multi-lens optical scanner," which as shown on FIG. 1, has a lens set 12 that is driven along a slide bar 13 by a manual driver 11; changing optical resolution is accomplished by switching to different lens this way. Referring to FIG. 2, this "multi-lens optical scanner" has a motor 21 that drives a reduction gear assembly 22 which, in turn, moves the gear rack 23 and the lens set 24 to change lens and optical resolution. In optical scanning equipment, the relative position of elements is critical; a slight misaligmnent shall result in blurred images. The shortcoming of aforementioned "multi-lens optical scanner" is its difficulty in being aligned accurately. References:
1. R. O. C. Patent No. 232398 issued to Huang on Oct. 11, 1994.
2. R. O. C. Patent No. 235112 issued to Ma on Nov. 21, 1994.